Manufacture of sodium hydrosulphides



May 22, 1945. A. w. SADDINGTON MA'NUFACTURE OF SODIUM HYDROSULPHIDES Fild May 30, 1944 4 sheets-sheet 1 May 22, 1945. A. w. sADDlNGToN AMANUFAGTURE OF SQDIUM MHYDROSULPHIDES Filed May 30, 1944 4 Sheets-Sheet 2 hm@ Nunn AT'HNEY May 22, 1945 A. w. sADD|NGToN 2,376,435A

MANUFACTURE 0F SODIUM HYDROSULPHIDES May 22, .1945- A. w. sADDlNG-TON I 2,376,435

MANUFAGTURE OF SODIUM HYDROSULPHIDES BY W 42%@ :WHA/Er A Patented May 22, 1945 v MANUFACTURE oF sonnJM` maosunrmnas Arthur W. Saddin'lton, Syracuse, N. Y., assigner to The Solvay Process Company, New York, N. Y., a corporation o! `New York A Application May 3U, 1944, Serial No. 538,101

(Cl. 23-134l Claims.

This invention relates to improvements in the manufacture of sodium hydrosulphide (NaHS) or sodium sulphide (NazS) o r mixtures of both.

With the exception of a very small amount, all

,commercial grades of sodium sulphide are made` from salt cake (NazSOi)- or nitre cake (NaHSOi) by reduction with coal or coke at elevated temperatures. Reaction is usuallycarried out in re- 'verberatory or rotary furnaces, and the furnaced material is put thru a relatively elaborate and cumbersome NazS' recovery and` purification procedure. Such process is inherently complicated and-costly. and moreover results in .an end product containing a substantial quantity of impurities, particularly iron. Sodium hydrosulphide may be formed by gassing sodium sulphide liquor with hydrogen sulphide. Also, sodium `sulphide may be made by treating anVNaHS liquor with sodium hydroxide.

It `is known that ysodium carbonate (NazCOa) reacts with HzS to form NaHS. Attempts. have been made to produce NaHS by gassing a liquor containing sodium carbonate with hydrogen sulphide. While these proposals bring about formation of some NaHS which remains in solution, it was observed that theV proportion lof the sodium content of the liquor subjected to gassing which precipitated as a sodium acid carbonate (mostly NazCOaNaHCOaZHzQr and NaHCOs) was so great and the loss of sodium as precipitate was so high' as to render processes of such nature uneconomi cai. As far as known, there is no commercial production of sodium hydrosulphide or sodium sul-l phide by reaction of sodium carbonate and hydrogen sulphide.

A major object of this invention vlies in provision of a process for making sodium hydro- 4 sulphide or sodium sulphide, of purity acceptable to the trade, using as raw materials commercial grades of soda ash (NazCOa) and impure hydrogen sulphide gases which are readily available. Y commercially. Practice ofthe invention involves gassing an aqueous solution containing sodium carbonate with an Has gas to eiect reaction of ANazCOs and HzS to form NaHS. 'A chief object of the present improvements is provision of processes for carrying out the sodium carbonate liquor-Has gassing operation in such a way that there may be formed an HzS-NazCOa reaction product liquorV of high NaHS concentration. Other important features include provision of procedures by which (l) it is possible to prevent formation of carbonate containing solid phase which not onhr plugs up the Narco: liquor-Has loss of sodium as asodium acid carbonate of one kind or another, and (2) decomposition of sodium acid vcarbonate v lnecessarily formed during HzS gassingmay be eiiected to such an extent that the amount of sodium acid carbonate carried in solution in the liquors in the system is held at an g economical low level. Further purpose of the `the presence of which normally Vtends to increase formation of sodium acid carbonate.

While it is evident that sodium acid carbonates, which are formed and exist in solution and which tend to separate out in solid phase from liquors suchvas handled in the invention process, include sodium sesquicarbonate NaaCO3.NaHCOs.2H2O, and Adecimite Na2CO s.3NaHCOa, as well as a major amount of sodium bicarbonate itself, unless otherwise specified, mention of sodium`bicarbonate herein is intended, for convenience, to include all sodium acid carbonates-present.-

The process o f this invention scomprises generally three major stages: first, thepreparation of an NaHS liquor containing NazCOs and of certain composition with respect to NaHS and NaHCOz contents, and having a moderate total sodium salt content; second, a raising of the NazCOs concentration of such solution to bring about a corresponding increase of the total sodium salt content to a relatively high amount; and third,

a reaction stage in which the high total sodium salt conten liquor is gassed with HzS under certain conditions to form a liquor of relatively high NaHS concentration. In this specification' and appendedclaims, the expression total sodium salt content" is used to define the sumof any-or all of the sodium' salts of the group consisting of the carbonate, bicarbonate, bisulphida and sulphide of sodium. l -In the course of developments of which this invention-is a part, it was observed that a dependent relationshipbetween (1) the particular `composition ofi-,an initial aqueous sodium car,-

minimizes the amount of sodium acid carbonate gas contacting apparatus but also causes heavy l5 retained inthe product solutions. Among other tory ways.

features, it was found that the aqueous sodium y carbonate starting liquor shouldy have in solution a total sodium sall-l content of not more than 21% by weight, expressedas NazCOa.

I have discovered that if, as by the HzS gassing of -an initial sodium carbonate starting solution having a total'sodium salt content of not more than7 21% by weight expressed as NazCOa, there is formed a liquor having a, total sodium salt Aconten of not more than 21% by weight, and containing not less than by weight of `NaHS, not more than 14% of NaI-100s, along with variable amounts of unreacted Na2CO3, provided the NaHS content is not perf mitted to become reduced below 5% and the NaHCOa content is not permitted to become increased above 14%, it is then possible to materially`increase the total sodium salt content ture and pressure are adhered to, such a liquor may be gassed with HzS to produce a liquor having ahigh NaHS concentration, and at the same having an NaaCOa concentration of not less than 10% and not more than 21% by weight. Such a solution may be made up in tank I6 by adding the proper amount of commercial soda ash Vto water. The starting solution may contain. some y NaHS, some sodium acid carbonate, possibly time formation of carbonate containing solid phase is prevented and the'amount of sodium acid carbonate retained in solution in the product liquor is minimized. Viewed from another angle, I have found that an aqueous solution containing NazCOs, not less than 5% by weight of. NaHS, not more than 14% by weight of NaHCOa and having a total sodium salt content of preferably not less than 21% but not more than 29% by weight expressed as NazCOa,

may be gassed with HzS under the described reaction conditions without formation of carbonate containing solid phase or the presence of excessive amounts of sodium acid carbonate in the ultimate NaHS product solution. .By reason of the foregoing' discoveries, permitting substantial increase in the given liquor of the amount of NazCOa available for reaction with HzS, the invention affords a marked advantage of facilitating production of reacted liquors of high y Nal-IS concentration.V

may be carried out, and Figs. 2, 3 and 4 show apparatus in which modified-procedures may be practiced. v

All modifications of the invention involve formation-of aqueous solutions containing NazCOs, not less than 5% by weight of vNaI-IS, not more than 14% by weight of NaHCOa and having to total sodium salt content not more than 29% by weight, lexpressed as NazCOs, and subsequently gassing such solutions with HzS gas y under certain temperature and pressure conditions. These high "total sodium salt content solutions rnay be made up in several satisfac- In the embodiment of Fig. 1, such solutions are formed partly by preliminary HzS gassing of relatively low total sodium salt contentv starting solutions in the first two reaction zones i0 and Il of a system including three liquor-gas contacting towers I2, I3 and I4. In

this operation, the preferred starting solution is an aqueous NazCOs solution containing substantially no sodium salt other than NazCOa and some NazS, or some of any two or all three, but preferably the sodium salt present should be predominantly NazCOa as such, and in any case the total sodium salt content should not exceed 21% by weight expressed as NazCOs. The starting solutions usually employed are water solutions of sodium carbonate having NazCOs concentrations of 1820% by weight.

, In all liquor-gas contacting zones'inall modications of the invention, similar temperature out and discharge from the contacting zone`,of

CO2` initially combined with NagCOs and thus minimize the quantity of sodium acid carbonate held in solution in the liquor discharged from the contacting zone, the sodium carbonate-H28 gassing operation should be'carried out while maintaining, in the contacting zone, temperature not less than C. and not more than 125 C. Preferred operating temperatures are in the range of 10S-115 C., and very good results have I been obtained when reaction zone temperature is held-at about 10G-108 C.- Temperatures not less than 100 `C. are needed to prevent precipitation of carbonate containing solid phase, and speed up decomposition of sodiumY acid carbonate. While temperatures above C. maybe used, higherr temperatures are not preferred because of greatly increased equipment corrosion.

Another condition of importance during HzS gassing is regulating the contacting operation, in reaction zones Il) and Il so as to prevent, during reaction, lincrease of total sodium salt content of `the solution to more than 21% by weight, since in this phase of the process higher total sodium salt content should be avoided to prevent formation of carbonate containing solid phase. Such regulation of the contacting operation is dependentupon the "total sodium salt content 'of the particular starting solution used, and also upon the conditions at which any specific gassing operation is being carried out. As previously indicated, starting solutionsusually employedare those having a total sodium salt content (preferably all NazCOa) of the order of 18-20%. It will be seen that ,when utilizing such starting sclutions'there is not much latitude for solution prevent any substantial boiling of the solution being g assed.v Specific pressure to be used is.

dependent upon the particular temperature prevailing in the reaction zone. Solutionsof the type employed for HzS gassing'in accordance with the present invention have boiling point of the order of 105 C. Thus, if reaction zone temperature is say 10U-103 C., it is possible to proceed atatmospheric pressure without losing enough water vapor to cause detrimental total sodium salt concentration. However, preferred reaction temperatures are 105 C. or above, and

accordingly it is preferred to subject the solution l being gassed to superatmospheric pressure sumcient to prevent any substantial boiling to thus avoid loss of water vapor and corresponding total sodium salt content concentration. `Pressures up to 30 lbs. gauge maybe used, pressures inthe preferredV temperature range of 105115 l C. being about 5-20 lbs. gauge.

When using starting solutions having total sodium salt content substantially less than 21% by wei'ght, expressed as NazCOa, it should be un- A derstood that appreciable total sodium salt content concentration during gassing is permissible without increasing the total sodium salt content of the solution to more than 21%. Thus when using relatively weak, say of the order of total sodium salt content, starting solumay be permitted until the total sodium salt content approaches 21%.

While the gassing operation in general may be carried out in any satisfactory liquor-gas contacting apparatus, in the modiiicationof Fig. 1, it is preferred to eiect reaction in a plurality of countercurrent towers of suitable design. The towers may be packed, e. g. with suitably sized coke or say 1 inch Raschig rings, or packing may tions, boiling of the solution undergoing gassing volume.

50% Has by volume, and iffsuch gases contain CO2, concentration of the latter should bev not above 25% by volume, i. e. CO: content by volume is preferably not more than half the HzS content by volume. In usual operation, gases Vutilized comprise about 90% Has and about 10%' CO: by In" this speciiication and appended claims, unless otherwise indicated, gas compositions mentioned are intended to denne. compositions `of the HzS gas'at the point of :first contact of lincoming gas with `intermediate or ultimate product liquor leaving any particular stage. of the system, e. g. in Fig. 1, at the bottom of tower I3 or alternatively at the bottom of tower Il. The Hi8 employed is held at source 20 under pressure of say -40 lbs. gauge.

Purpose oi' towers I2 and I3 is to produce, in eilluent liquor line 2l of tower I3, a sodium hydrosulphidev` liquor containing NazCOs, not less than 5% by weight of NaHS, and not more than 14% NaHCOs, preferred liquor compositions at.

this point being 8-14%-of NaHS and not more than 10% of NaHCOs. As above indicated, I iind that until the NaHS `and Nal-ICO; concentrations ofthe liquors in the system have been brought to the 5% and 14% values stated, total equivalent NaaCOa content should not exceed 21% by weight. Hence, the soda ash starting solution fed into tower I2 from tank I6 should not contain more than 21% equivalent NazCOi. Ordinarily valves 25 and 26 are closed, since necesenters the bottom of tower` I1 from pipe 36, and

duction of liquor into the top of a reaction zone v against whatever pressure there may be therein.,-`

control of rate of feed of' incoming liquor, discharge of reacted liquor, recirculation of liquor over all or part of the tower if desired, maintenance throughout the contacting Vzone of the indicated temperatures and whatever pressures may be' needed, introduction into the reaction zone of HzS gas employed, and discharge of tail gas. Temperatures may be maintained by controlled indirect heating not shown, e. g. a heating jacket' around each tower, and pressures in the system may `be regulated largely by adjustment .of valve 8 at the His gas source 20 and of valve I9 in the tail gas line 2 I, f

VIn practice, the gases which may be employed include pure HaS gas, HzS gas containing diluents inert to the reaction, or an I-InS gas containing a diluent such as CO2 which is not inert to the reaction, i. e. CO2 reacts in water'solution with NazCm to form NaHCOs. In the case of HnS gases containing diluents inert to the reac- -tion, Has concentration may be anyieasiblex value. In order to prevent a build-up of NaHCOa f in the system, particularly in a continuous operation, if the HzS gas used contains Q02, such incoming HzS gas shouldcontain by volume not more CO: than' HzS. In all operations, it is preof water vapor.

gas of the same HzS strength is fed into the bottom of tower I4 by conduit 31, relatively Vstrong HiS gas thus passing in parallel thru towers It `and I4. The exit gases of towers I3 and` Id are combined in conduit 40 and introduced into the bottom of tower I2, and the combined gasmay contain from 10 to 30% HzS and from 90 to 70% G02 and possibly some relatively small amount Bythis procedure, the gas in the system having the lowest Has concentration 4is contacted, in tower I2, with liquor of relatively high NazCOs concentration, thus providing for `over-all utilization of about {l5-98% of the total vHri. i

15% NaHCCa, and 'I t0 11% NagCOr. Since pri-v mary function of tower I2 is to aii'ord good cleanup of HzS, degree of conversion of NazCCa to NaHS is not critical. If desirable to build up the NaI-IS concentration of liquor discharged `from tower I2 to say 5-8%, valve 25 may be opened and a portion of the liquor `continuously recirculated. According to one example, using an aqueous starting solution f'containing 20% by weight of NazCOa, and a gas from pipe 40 containing 20% H28 and 80% CO2, the eilluent *liquor` 'in pipe 28 may contain by weight 5%: NaHS, 12%

NaHCO, and 9% NazCOs.' l

Partially reacted liquor formed in tower l2 is fed into the top of tower Il thru pipe 44 and is contacted countercurrent with relatively strong When utilizing `a gas containing liquor.

HzS gas. Overall gas contacting operations in towers I 2 and I3 are preferably conducted so that the eiuent liquor of tower I3 in line 24 has an NaHS concentration of say 12-16% by weight, vin which instance such liquor may contain from 3 to 7% NaHCOa and 3 to 6% NazCOa. 1f, as is ordinarily the case, fairly high NaHS and relatively low NaHCOxy concentrations are desired in line 24, valve 26 may be opened to effect recir-V in connection with formation of carbonate containing solid phase. in towers I2 and I3. Hence, it will be .understood that even though liquors are recirculated over towers I2 and I3, the total sodium salt content of the liquors in the system upto and including pipe 2liv does not significantly exceed 21% by weight, expressedas NaiCOsiv Result' of the foregoing operation of towers I2 and I3 is production'and feed to tank 3I of liquors relatively depleted of available NazCOa and having NaHS concentration Well above by weight, and NaHCOs concentrations well below 14% by weight. In accordance with the invention, I find that, provided the NaHS content is not permitted to drop below 5% and the NaHCOa content is not permitted to exceed 14%,the total'sodiuin salt content of the liquor may beincreased to 29% by Weight, expressed as NazCCs, and the resulting liquor may be gassed further with HzS to form a reacted liquor having a high NaHS concentra-V tion. i

While raising NazCOs concentration and increasing total sodium salt content of the ing operation is regulated so as to prevent increase of total sodium salt content of the solustantially lower total sodium salt content, e. g.

23-24%, boiling ls permissible until total sodium salt content approaches 2728% Design of ,tower I4 and rates of feed of liquor and HzS gas thereto may be such as to produce in pump tank 52 a reacted liquor containing NaHS froml 18 to 23%', NazCOa from 3 to 6%, and NaHCOa from 2 to 5%. take off from pipe 53 a liquor having the-highest feasible NaHS concentration, it may be desirable to recirculate thru tower I4 part of the liquor from tank 52, in which case valves 54 and 55 are suitably adjusted. In the example given, the liquor in tank 52 may contain by Weight 23% NaHS, 2% NaHCOs, and 4% NazCOs.

' As indicated, the reacted liquors in lineA 53 con- .tainappreciable quantities of sodium acid carliquor may be ,effected in more than one way, it. I

l is preferred to accomplish this endby introduction into the system of extraneous NazCOs. Ad-v ditional Na2CO3 is supplied preferably as dryA t soda ash, although such NazCOa may be introduced in the form of strong solutions or slurries having an NazCOs concentration as much in excess of 29% by weight as feasible. Whenftotal sodium salt content is increased by addition of extraneous NazCOs, there is some decreaseof the NaHCOa and NaHS contents in the resulting Accordingly, to prevent ldrop of NaHS content below 5% during addition of the extrabonate and sodiumI carbonate, NazCOa. Liquors of this type cannot be concentrated by the usual evaporation methods in the presence of sodium acid` carbonate, without loss of NaHS, since it appears that on heating, sodium acid carbonate causes decomposition of NaHS withre'sultant formation of Na2CO3 and H28.' Hence, sodium acid carbonate should be removed substantially completely from the reacted liquor in any suitable way. This may be accomplished, for example, by treating liquor from tank 5'I with caustic soda, resulting in conversion of sodium acid carbonate to NazCOs and Water. Following substantial elimination of sodium acid carbonate, the liquor may be concentrated as desired to strength of about 50% NaHS in an evaporator not shown. During such concentration, which may be eliected by heating the liquor at atmospheric pressure to about 150 C., most of the NazCOa precipitates, settles out and may be removed by filtration. The resulting relatively strong NaHS iiltrate ordinarily contains in solution about 0.2-0.3% NazCOs in solution, which' residual NazCOsmay be removed in any suitable way if a substantially pure NaHS end product is desired. If the end product def sired is N azS, the NaHS liquor may be treated with NaOH to convert all or any portion of the NaHS to NazS. Alternatively, NaHS or NazS may be produced in solid form by evaporation of the `liquors' and solidication by known methods.

neous NazC'Os, towers I2, and I3 are usually operated to produce an intermediate liquor of such NaHS strength above 5% that during addition of .operation in towers I2 and I3 and the mixing in tank 3| are regulated so that the liquor fed into i the top of tower I4 thru pipe 50 contains-not less than 5% by 'weight of NaHS, not more than 14% by weight of NaHCOs, and has a total sodium salt content notmore than 29% and pref,- ably more than 21% by weight. `In the example under consideration, the quantity of dry soda ash used may be such as to form in tank 3I'a liquor NazCO; by-product may be returned to the process.

:Increase of total sodium salt content to not more than 29% by weight may be accomplished tions asin cases where the. apparatus arrangement is such' that the HzS gas passes in series v thru towers 13, I I and 'I0 in the orderv named.

containing by weight 12%I NaHS, 4% NaHCOg.

and 15% NazCOs.

Operation of tower I4 is the same as thatof When using a 20% by weight soda ash water solution and introducing into the bottom of tower I0 from. line 15 a gas containing 10% H25 and Y is treated in tower 'II with a gas from pipe 'I9 f Where lt is desired to In accordance with this modication, raising of the total sodium salt content is had by evap' oration and concentration of the eiiluent liquor of tower 1|, and to this end the liquor in pipe 80l l is heated at temperatures of the order of G-125 C., NaHCO reacts with NaHS with formation of NazCOs and HzS. Hence, if precautions are not taken to offset NaHS decomposition in the evaporating step, the NaHS content of -the liquor Y might fau below 5%, and an appreciame amount of HzS would be lost in the 'gas-vapor exit of the evaporator. To overcome this difficulty, during evaporation, a quantity of gas containing e. g. 90% HzS and 10% CO2 from pipe 84 is fed into the evaporator. The quantity of HZS introduced is such, under the particular conditions of operation, to maintain a pressure of HzS in `the gas phase at least equal toand preferably in excess of the HzS partial pressure of theA solution. In

any particular operation the quantity of HaS used Amay be gauged by the composition of the gasvapor exit of the evaporator, admission of HaS being so controlled that the gas-vapor exit contains substantially no I-IzS.A

Result of the evaporator operation is removal of water from the.system, prevention of decomposition of NaHS,`increase of NaHS and NaaCOa contents ofthe liquor, and a substantial decrease l of theNaI-ICOa content of the liquor which detower 1| may be such as to produce in pipe 88 an eiiluent liquor containing by weight 9% NaHS, 9%- NaHCOs, `6% vNazCOa and having a"t0tal sodium salt content of about20% by weight, i. e. operation of tower 1| of Fig. 3 being the same as the operation of tower 1| of Fig. 2. However, in the process of Fig. 3, the total sodium salt content of the intermediate productliquor is increased partly by sodium brought in as NaOH,

and partly by sodium brought in as NazCOs, both being introduced preferably in dry form. NaOH reacts with NaHCOs to form NazCOa and liberate The quantity of NaOH used is preferably not more than that needed to react with the .NaHCOa present, thus avoiding undesirable rehas a total sodium salt content, e. g. 2'728%,`

not more than 29%. Operation of tank 89 is such that the liquor in pipe 90 may contain by weight 9% NaHS; 3% NaHCOa, 17% NazCOa, and havea total sodium salt content of about 27% by weight, expressed as NazCOa. :Such liquor is then treated in tower 13 of Fig. 3 with gas containing 90% HzS and 10% CO2 to form a product liquor `of composition similar to the eiiiuent liquor of tower' 13 of Fig. 2. l

In the modification of Fig. 4, the major portion of NaHS liquor production is effected in a single reaction tower 92 normally functioning in conjunction with a relatively small HzS clean-up Ytower 93. In starting up operations, valves 94, 95, 98, 91 and 98 are closed, and valves |00, |0| and |02 Aare opened. The system including mix tank |04,.pipe |05, tower 92, pump tank |06 and returnpipe |08 is filled with a starting solution similar to that of tank I6 of Fig. 1, e. g. a water solution containing about 20% by weight of NazCOa. This solution is treated in tower 92 with a gas containing say 90 HzS and 10% CO2, under the previously described temperature and prescrease is caused by the decomposition of NaHCOa to NaaCOa. Liquor retention time depends largely upon the design of the evaporator andupon the total sodium salt content of the liquor charged thereto. If desired, the evaporator may be of tower-like construction and be provided with liquor recirculating means. In any case, retention time is regulated so that total sodium salt content of the 4liquor is raised to not more than 29%. In the case of introduction into evaporator 82 of a liquor of the composition indicated in pipe 80, and adjusting the amount of. HzS introduced so that the gas-vapor exit contains substantially no HzS, the liquor leaving thru pipe |33` may con- `tain by Weight 12% NaHS, 3% NaHCOs, 14%

NazCO: and have a total sodium salt content of about 27% by weight, expressed as NazCOa. Such liquor is then run thru pipe 85 into the top of tower 13, treated with 90% Has-10% CO2 gas as previously described, and product liquor leaving tower 13 thru pipe 81 may contain by weight 20% Nans, 2% NaHco, '1% Nazcog, and have a sure conditions. Such gassing is continued until the liquor circulating thru tank |04 and tower 92, having a totalsodium salt content of about 20-21% by weight, contains not less than 5% by weight NaHS and not more than 14% by weight NaHCOs, and ordinarily until such liquor contains by weight 8-14% NaHS and not more than 10% NaHCOs. Total sodium salt content may be then raised to an amount 'not more than 29% by weight, and for this purpose a suitable quantity of preferalbly `dry NazCOc or NaOI-I or some of both vis introduced into tank |04. If NaOH is employed, the quantity used is preferably riot more than that needed toreact with the NaHCOa present in order to avoid undesirable reaction of NaOH and NaHS. Valves 94 and 95 are then closed, and the liquor is gassed intower 92 and recirculated thru tower 92 and tank |04 until theI l top of tower 92 and entering the bottom of tower "total sodium salt content of about 27% by weight.

In theembodiment of Fig. 3, the gas entering the bottom of tower 1| from pipe19 may contain 50% HzS and 50% CO2, and operation of 93 by pipe ||2 may be recovered by countercurrent contact in tower'93 with starting solution from' tank ||0, the resulting eluent pf towerI y 93. being temporarily stored in apparatus not shown, v

With valves 90, 91 and 98 open, and say valve $5 partly open, the normal production operation weight, expressed as NazCOs.

.l maybe initiated. Part of the high NaHS concentration product liquor is drawn off thru valve 91, and an equal volume of starting solution isy fed into the top of tower 93 from tank l I0. When I introducing into the bottom of tower92 a-gas containing about 90% HzS'and 10% CO2, the gas discharged from tower 92 into pipe l|2 ordinarily contains about 10% HzS and 90% CO2. With a weak gas of this nature entering tower 93, the liquor effluent in pipe H4 is rather low in NaHS, and relatively high with respect to NaHCOx content, and the composition of such liquor may be of th'e order of 2 to 6% NaI-IS, l0 to 15%` NaHCOa,

and '7 to 12% NazCO-i, fby weight. It will be understood that the temperature and pressure conditions maintained in tower 93 are the same as in tower 92. Accordingly, the total sodium salt content" of liquor in pipe I I I `is not increased and is held to about 2021% by weight, expressed asv NazCOa.

Product liquor in rpipe |09 may contain by weight 23% NaHS, 2% NaHCOs, 5% NazCOa, and may have a total sodium salt content of about 2'7-28% by weight. Liquors from pipes |08 and v I Il are continuously fed into tank |04, and the quantity of product liquor run into tank |04 fromv would be decreased and be substantially less thany the preferred 2'7-28%.` Hence, enough extraneous sodium (in the form of NaOH or NazClOa lor both) is vcontinuously introduced into tank |04 to maintain the '"total sodium salt content" of the liquor in tank |04 at about 27-28% by When proceeding in this manner, there is fed to the top of tower 92 a liquor which may contain by weight 10% NaHS, 1% NaHCOa, 16% NazCOs, and have a total sodium salt content of about 28% by weight. Under some conditions of operation, the NaHCOs content of the liquor in line ||4 might be high enough to cause the NaHCOa content of the composite liquor in tank |04 to approach too closely the indicated maximum of 14%. Insuch circumstance, sufficient NaOH should be used to keep the NaHCOa content of the liquor in tank 04 at aconvenient operating point below 14%.

Thus, normal practice of the embodiment of Fig.4 involves continuous formation in tank |04 of a composite liquor containing a relatively large quantity of NaaCO` available for reaction with HsS to form sodium hydrosulphide, not less than 5% by weight oi' NaHS (preferably not less than 8%gby weight NaHS), not more than 14% by weight NaHCOs (preferably not more than 10% Since the fine "total sodium salt content in terms of percent by weight expressed as NazCOa.

Two copending applications, of Julien and Terziev, Serial No. 522,794, and Charles L. Koenig, Serial No. 527,143, both assigned to thel same -common assignee as this application and both directed to subject matter related to this application, were filed on February 17, 1944, and March 18, 1944, respectively.l l l I claim: i l 1.v The method -for producing sodium hydrosulphide which comprises forming an aqueous solution-containing NazCOz, not less'than 5% byv weight ofl NaHS, not more than 14% .by weight of NaHCOa, and having a total sodium salt content notlless than 21% and not more than 29% by weight, contacting said solution with gas containing HzS and an amount of COz ranging from none to a volume equal to the volume of the HzS content of said gas, and maintaining, during said contacting operation, temperature not less .than 100,` C., and pressure conditions such as to prevent any substantial boiling of said solution,l thereby forming relativelyconcentrated sodium hydrosulphide solution. Y A

2. The method for producing sodium hydrosulphide which comprises forming an aqueous solution containing NazCOs, not less than-8% by weight offNaHS, not more than 10% by weight of'NaHCOs, and having a "total sodium salt content" not less than 21% and not more 'than 29% by weight, contacting said solution with gas containing HzS and an amount of CO2V ranging from none `to a volume equal to the volume of the HzS content of said gas, and maintaining, during said contacting operation, temperature not less than 100 C., and pressureconditions such as to,

prevent any substantial boiling of said solution, thereby forming relatively concentrated sodium hydrosulphide solution;

3. I'he method for producing sodium. hydrosulphide which comprises forming an aqueous' solution containing NazCOs, not less than 5% by weight of NaHS, not more than 14% by weight of NaHCO3, and having a total sodium salt content not less than 21% and not more than 29% by weight, .contacting said solution with gas containing HzS and an amount oi' CO2 ranging from none to a volume equal to the volume of the HaS content of said gas,l and maintaining, during said contacting operation, temperature not less than 100 C. and not more than 125 C. and pressure conditions such as to prevent any substantial boilingof said solution, thereby forming relatively concentrated sodium hydrosulphide solution.

4. The method for producing sodium hydrosulphide which comprises forming an aqueous sclution ,containing NazCO, not less than 5% by by weight NaHCOa) andhaving a "total sodium salt content not less than 21% and not more than 29% by weight, expressed as NaaCOa. By proceeding as indicated, a. reacted liquor having the highest feasible maximum concentration oi' NaI-IS may be continuously drawn out of the system thru valve 91.

weight of NaHS, not more than 14% by weight of NaHCOa, and having a total sodium salt content n'ot less'than 21% and not more than 29% by weight, contacting 4said solution -with gas containing HzS and an amount of CO2 ranging from none to a volume equal to the volume of the H28 content of said gas while maintaining temperature not less than C., and regulating the conl" y' tacting operation so as to prevent, during the course thereof, increase of total sodium salt content" of the solution undergoing HzS gassing to more than 29%, by weight, thereby forming relavely concentrated sodium hydrosulphide soluon.

5. The method for producing sodium hydrosulof NaHCOs, and having a "total sodium salt conten not less than 21% and not more than 29% by.weight, contacting said solution with gas containing HaS and an amount of CO2 ranging from none to a volume equal to the volume of the HzS content of said gas while maintaining temperature not less than 100 C., and regulating the contactingv operation so as to prevent, during the course thereof, increase of total sodium salt content of the-solution undergoing HzS gassing to more than 29% by weight, thereby forming relatively concentrated sodium hydrosulphide solution.

6. The method for producing sodium hydrosulphide which comprises forming an aqueous solution containing NazCOanot less than 5% by `weight of NaHS, not more than 14% by weight of Nancos, and having a "total sodium' sau content not less than 21% and not more than 29% by weight. contacting said solution with gas containing HzS and an amount of CO2 ranging from none to a volume equal to half the volume of the HzS content of said gas, and maintaining temperature not less than 100 C. and not more than 125 C. and pressure conditions such as to prevent increase of total sodium salt content of the solution undergoing H25 gassing to more than 29% by weight, thereby forming relatively concentrated sodium hydrosulphide solution;

7. The method for producing sodium hydrof sulphide which comprises vforming an aqueous solution containing NazCOa, not less than 5% by weight of NaHS, not more than 14% by Weight of NaHCOa, and having a total sodium salt content not more than 21% by weight, increasing the total sodium salt content to not more than 29% .by weight while maintaining NaHS content of the solution not less than 5%r and NaHCOs content not more than 14% by weight, contacting the resulting solution with gas containing HzS and an amount of CO2 ranging from none ato a volume equal to the volume-of the H2S content of said gas while maintaining temperature not less than* 100 C., and regulating the contacting operation so as to prevent, during the course thereof, increase of total sodium salt content of the solution undergoing HzS gassing to more than 29% by weight, thereby forming relatively concentrated sodium hydrosulphide solution. i l

8. The' method for producingsodium hydrosulphide which comprises forming an aqueous solution containing NazCOa, not less than 5% by weight of NaHS, not more than 14% by weight of NaHCOs, and having a total sodium salt content not `more than 21% by weight, raising the NazCO'a concentration of saidsolution and increasing the total sodium salt content thereof to not more than 29% by weight while maintaining NaHS content of the solution not less than 5% and NaHCOs content not more than 14% by by weight of NaHS, not more than 14% by weigh of NaHCOs, and having a "total sodium salt content not more than 21% by weight, adding 4extraneous NazCOs to said solution to increase the total sodium salt content thereof to not more than 29% by weight while maintaining NaHS content of the solution notless than 5% and NaHCOs content not more than 14% by weight, contacting the resulting solution with' gas cntaining HzS and an amount of CO2 ranging from none to a volume equal to the volume ofthe HzS content of said gas while maintaining temperature not less than 100 C., and regulating the contacting operation so as to prevent, during the course thereof, increase of ftotal sodium salt content of the solution undergoing HzS gassing to more than 29% by weight,thereby forming relatively concentrated sodium hydrosulphide solution.

10. The method for producing sodium hydro- ,of the solution not less than 5% and NaHCO:

content not more than 14% byweight, contacting the resulting solution with gas containing HzS and an amount of CO2 ranging from none to a volume equal to the volume of the HzS content of Asaid gas while maintaining temperature not less than 100? C., and regulating the contacting operation so as to prevent, during the course thereof, increase of total sodium salt content of the solution undergoing l- IzS gassing to more than 29% by weight, thereby forming relatively concentrated sodium hydrosulphide solution.

ll. The method for producing sodium hydrosulphide which comprises forming an aqueous soluton containing NasCOa, not less than 8% by weight o f NaHS, not more than 10% by weight we'ght, contacting the resulting solution with gas containing HzS and an amount of CO2 ranging from none to a volume equal to the volume of the HzS content of said gas while maintaining 'temperature not less than 100YC., and regulating the contacting operation so asto prevent, duringtliecourse thereof, increase of total sodium salt content of the solution undergoing HzS gassing to more than 29% by.weight, thereby formng relatively concentrated sodiumhydrosulphide solution.. y i i l9. The method for producing sodium hydrosulphide which comprises forming an aqueous solution containing Na'zCOz, not less than 5% of `NaHCOs, and having a "total sodium salt content not more than 21% by weight, adding dry NazCOa to said solution -to increase the "total sodim s altcontent thereof to not more than 29% by weight while maintaining NaHS content of the solution not less than 8% and NaHCOt' Crand not more than 125 C. and pressurei conditions such as to preventA any substantial boiling of said solution, thereby forming relatively concentrated sodium hydrosulphide solution. f l

12. The method for producing sodium hydroi sulphide which .comprises forming an aqueous solution containing NaaCOs. not less than 5% by weight of NaHS, not more than 14% by weight of NaHCOs, and having a total sodium salt content not morev than 21% by weight, evaporating the solution to increas the total sodium salt content thereof to not more than 29% by weight, said evaporation operation being carried out in the-'presenceof sufficient extraneous lHzS to maintain a pressure of gas phase H28 at least equal to theHzS partial pressure of the solution, contacting the resulting solution. with gas containing Has and an amount of CO: ranging from none toy a volume equal to the volume of the HzS content of said gas-while maintaining temperature not less than 100 C., and regulating the contacting operation so as to prevent, during the course thereof, increase 'of total sodium salt conten of the solution undergoing H28 gassing to more than. 29% by weight, thereby forming Y relatively concentrated sodium hydrosulphide solution.

13. The method for producing sodium hydrosuiphide which comprises forming an aqueous solution'containing NazCO's, notles's than 8% by weight of NaHS, not more than 1,0% by weight of NaHCOa, and having a total sodium salt content not more than 21% by Weight, evaporating thesolution to increase the total sodium salt content? thereof to notmore than 29% by Weight,

`concentrated sodium hydrosulphide solution.

14. The method for producing sodium hydrosulphide which comprises forming an aqueous NazCO solution containing substantially no sodium saltother than NazCOs and having an NazCOa concentration not less than'10% and not more than 21% by weight, contacting said solution with HzS gas while `maintaining temperature not less than 100 C., and regulating the contacting operation so as (1) to prevent, during the course thereof, increase of the total sodiumL salt content of the solution undergoing HzS gassing to more than 21% by weight, a.'nd (2) to form a sodium hydrosulphidesolutin containing not less than 5% by Weight of NaI-IS and not more than 14% by weight of NaHCOs; raising the NazCO: concentration of said sodium hydrosulphide solution and increasing the total sodium salt content" thereof to not more than 2,9% by weight while maintaining NaHS content of `the solution not less than 5% and NaHCOs content not more than 14% by weight; contacting the resulting solution with gas containing HzS and an amount of CO2 ranging froml none to a volume equal tothe volume of the H25 content of said gas by .maintaining temperature not less `than 100 C., and regulating `saidsecond mentioned contacting operation so as to prevent, during the course thereof, increase of total sodium salt content of the solution undergoing HzS gassing to more than 29% by Weight, thereby forming relatively concentrated sodium hydro- 'sulphide solution.

15. The method for yproducing sodium hydrosulphide which comprises forming an aqueous `NazCOa solution containing substantially nosodium salt other than NazCO3 and having an NazCOa concentration of l8-21% by weight, contacting said solution with gas containing H2S and an amount of CO2 ranging from none to a volume equal to the volume of the H28 content of said gas while maintaining temperature of 10U-125 C. and pressure such as to prevent any substantial boiling of said solution, continuing `said contacting operation until the sodium hydrosulphde solution formed contains not less than 8% by l weight of NaHS and not more than 10% by weight of NaHCOa; adding dry NazCOa to said sodium hydrosulphide solution to increase the total sodium salt content thereof to not more than 29% by weight while maintaining NaI-IS content of the solution not less than 8% and NaHCOa content not more than 10% by weight; and contacting the resulting solution with HzS under temperature, pressure and HzS gas composition conditions above stated in connection .with the rst mentioned contacting operation,

thereby forming relatively concentrated sodium hydrosulphide solution.

ARTHUR W. SADDINGTON. 

